Air springs, as they are used for spring suspended wheel mounts, include essentially a rolling-lobe flexible member delimited by a cover plate (conical plate) on the one end and by a roll-off piston at the other end. An air spring volume is enclosed in the interior space of the rolling-lobe flexible member. The flexible member itself is made of rubber or a rubber-like plastic having attachment beads at respective ends thereof. In this connection, reference can be made, for example, to German patent publication 2,905,791.
The end of the flexible member disposed at the cover plate is usually attached by a bent-over edge. For this reason, the upper cover plate is also referred to as a bent-over edge plate. The lower edge of the flexible member or lower beaded end is usually configured as a cone provided with sealing grooves in order to be threadably engaged to a multi-part roll-off piston. The lower beaded end is provided with a clamping plate.
An air spring flexible member with a clampable sealing bead is shown in FIG. 1 of U.S. Pat. No. 5,269,496. The sealing bead is held by a bent-over edge of an upper attachment part configured as a bent-over edge plate and is clamped so as to be seal tight.
Furthermore, air springs are known wherein the end of the flexible member facing toward the roll-off piston is attached by bending over an edge. According to German Patent 1,039,375(corresponding to U.S. patent application Ser. No. 521,031, filed Jul. 11, 1955), the lower bead of the air spring flexible member is fixedly connected with that of the roll-off piston. The cylindrically-shaped roll-off piston is arranged along the same axis as the flexible member and ends in an end flange which is bent over to clamp about the bead and presses this bead against the annular edge of a cover. This cover closes the guide body and closes off the guide body relative to the flexible member. The bent-over edge is laid over the bead of the flexible member.
The roll-off piston disclosed in German patent publication 298 08 109 does have such an additional cover or clamping plate applied to the roll-off piston. Here, the piston part comprises a form body configured as one part and is connected via a bent-over edge to the flexible member so that the external peripheral wall of the roll-off piston is bent over inwardly to attach the end of the flexible member facing toward the roll-off piston. The corresponding end of the flexible member includes a bead-like annular portion which is engaged over by the bent-over edge. The annular portion is provided with a reinforcement insert.
Practical experiments for manufacturing air springs of this kind have shown that problems occur with the attachment of the flexible member to the open piston. The bead of a flexible member, which is usually formed thereon, cannot be used easily at the open roll-off piston. The sealing surface lies horizontally for a bead at the upper cover plate in order to be pressed against the upper cover plate when bending over the edge. The roll-off piston has, however, no end plate which usually serves as a counter holding surface. For this reason, the principle of bending over an edge (which is known from the horizontal cover plate) cannot be transferred to the attachment of the lower edge portion of the flexible member. A tilting of the bead by 90xc2x0 is also not possible because the flexible member is produced in a mold and the occurring backcut does not permit the part to be removed from the mold (FIG. 4).
To overcome the above problems in connection with the attachment of the flexible member on an open roll-off piston by bending over a flange, the following list of requirements has been set up: the special configuration of the piston-end bead must be of such a nature that a contact of the bent-over edge with the flexible member takes place as late as possible when bending over the edge in order to avoid the bead from escaping downwardly into the free space. When the bead engages, the bent-over gap must already be so far closed that the bead can no longer slip out therefrom. The bead must immediately lay in clamping contact against the inner surface of the contact wall.
In view of the above, it is an object of the invention to configure the end of the flexible member, which faces toward the piston, so that it can be reliably connected with a bent-over flange also with a piston open at the end thereof.
The rolling-lobe air spring of the invention includes: a bendable cover plate; a roll-off piston; a rolling-lobe flexible member defining a longitudinal axis and having a first end connected to the bendable cover plate and having a second end facing toward the roll-off piston; the rolling-lobe flexible member having a bead formed on the second end and the bead having a sealing surface for contact engagement with the roll-off piston; and, the bead being formed on the flexible member by vulcanization in such a manner that the sealing surface lies tilted at an angle (xcex1) with respect to a perpendicular to the longitudinal axis.
According to a feature of the invention, the piston-end bead portion can be connected with a bent-over flange connection to a one-piece sheet metal roll-off piston without additional attachment parts such as a clamping plate and the like. This contributes to a reduction of the components of the overall system.
The piston-end bead of the flexible member is configured at 45xc2x0 to the horizontal so that no backcuts are present either at the mold for vulcanization or on the product. In this way, no forming difficulties result. The bead is thereby so stable as to its form that a roll-off piston can be connected thereto with a bent-over edge portion. A backcut or undercut is a detail in a molded piece which is larger thatn the opening of the mold. Undercuts are also referred to as a backtaper and are explained, for example, in the test xe2x80x9cPlastics Technical Dictionaryxe2x80x9d of A. M. Wittfoht, published by Hanser International (1983), page 204.
The bead configuration having seal surface inclinations between 45xc2x0 and 65xc2x0 have been shown to be especially advantageous. The bead pivots into a 90xc2x0 position to the horizontal with the inwardly-directed process of bending over the edge portion.
The reduction of diameter in the lower region of the flexible member is only necessary for facilitating the formation of the rolling lobe during operation of the air spring flexible member. The diameter of the bead core and the diameter of the piston wall are matched to each other.